In both traditions repopulation after the flood is not biological but liturgical: the survivor's post-landing sacrifice is the literal manufacturing step for the next humanity. The new race is produced by ritual from inert material (thrown stones; poured offerings), and both texts pause to etymologize the result — Greeks from laas, mankind as 'the race of Manu' (mānava).
Deucalion lands on Parnassus and his first act is sacrifice — to Zeus Phyxios, 'god of Escape.' The sacrifice is answered by Hermes with a wish; Deucalion asks for people, and the stones he and Pyrrha throw over their heads become men and women (laos 'people' from laas 'stone').
Manu, alone after descending the slope thereafter called 'Manu's descent,' is 'desirous of offspring' and 'engaged in worshipping and austerities'; he performs a pāka-sacrifice of butter, milk and curds, and from the offering itself a woman, Iḍā, is produced within a year — 'through her he generated this race, which is this race of Manu.'
Frazer's Apollodorus 1.7.2 verified at Perseus ('the stones which Deucalion threw became men, and the stones which Pyrrha threw became women'); SB 1.8.1.7–10 verified at wisdomlib ('a woman was produced in a year... through her he generated this race'). Mountain-landing frame shared with Nimush/Ararat/Mauna Kea.
Our fact-checkers corrected the first draft:
Both traditions name a single non-human intermediary who fetches fire DOWN from heaven for mortals, and both hide the fire inside a plant in transit: latent in the araṇi wood until rubbed out; smoldering in the fennel pith until delivered.
In both, heaven never announces the flood openly.
The serpent as impounder of water: in both, the serpent takes the waters into its own keeping (encompassed under Vritra's bulk / swallowed into the Bakhu serpent's body), the world's motion stalls (the rivers penned like cattle / the solar barque standing still), and an armed god compels restitution · the waters are given back in full and flow resumes.
The water rises when human blood enters it · and gives back what it takes.